1. Field of the Invention
This invention relates to a process for extraction of radium from naturally occurring radioactive material (NORM)-containing materials such as scales, sludges, soils and sediments in which the NORM (radium), and any carrier, such as barite, which may be present, is first dissolved, then separated from NORM-free solids and then precipitated along with a carrier (barite). The process provides the NORM-containing barite as individual crystals of a size and shape that allows injection as a slurry through sandstone. This process is particularly useful for the treatment of NORM-containing scales, sludges, soils and sediments present in oil fields, particularly from drums, vessels and pipe, including pipe in wells or buried pipe, thereby providing an alternative to disassembly and hydro-blasting of these systems.
2. Description of Prior Art
The U.S. oil and gas industries generate up to 700,000 tons per year of materials that contain naturally occurring radioactive materials (NORM). Storage and disposal of large quantities of low level NORM-contaminated scale in the oil and gas industry is a difficult and expensive proposition. What is needed is a method to reduce the volume of the material generated by these industries, thereby making handling and disposal of these materials more efficient.
Radium-containing material, which is the NORM problem associated with oil and gas production, is found in three general forms. Material containing modest levels of radioactivity, ranging from very low to over 20,000 picoCuries per gram are found in pipe scale and in production equipment. This scale is usually, but not always, barite and other sulfates, and sand. Lower levels of radioactivity, from very low to about 2,000 picoCuries per gram are found in sludge in tank bottoms and pits. This material often contains substantial quantities of oil, water, iron corrosion products, sulfate and carbonate scales, and sediments. Finally, very low levels of radioactivity, usually less than 200 picoCuries per gram are found in contaminated soils.
The most common disposal method for NORM-containing waste is to encapsulate it in pipes and place these pipes between cement plugs in abandoned wells. In some cases, the amount of NORM-containing material is too great for this to be economical or practical. Concern also exists about casing collapse and long-term containment.
NORM-containing waste has also been mechanically ground and injected at pressures above the fracture pressure into some off-shore subsurface formations. Mechanical grinders used for this purpose grind the material to sizes as low as 10 microns in diameter. However, this is still large relative to the pore throat diameter in typical sandstone formations.
NORM-containing waste is also commonly packed in drums for on-site and off-site storage until a suitable disposal opportunity is found. Many thousands of such drums have accumulated at such storage facilities.
Conventional means for removing NORM from vessels and pipe systems comprising heavily encrusted iron is by disassembly of the vessels and/or pipes, often by cutting, and hydro-blasting the encrusted material from the vessel and pipe surfaces, followed by scraping and hydro-blasting of the vessels and pipes. Where disassembly and hydro-blasting of the encrusted material is not feasible, such as for pipes in off-shore oil wells, expensive chelating agents are used. These same chelating agents have been proposed for scale, sludge, and soil treatment. For example, U.S. Pat. No. 4,973,201 teaches the treatment of NORM in surface layers of the earth with an aqueous chemical composition including a polyaminopolycarboxylic acid (chelating agent) such as ETDA or DTPA in combination with a synergist, preferably oxalate or monocarboxylic acid anion such as salicylate which increases solubility of sulfates in an aqueous solution. In contrast to the process of the invention disclosed herein, the process taught by the '201 patent is slower and more than an order of magnitude more expensive. Similarly, U.S. Pat. No. 4,917,825 describes the actions of an organic chelating agent that is more selective toward radium than ETDA. In particular, the '825 patent teaches a solvent composition of an organophilic carboxylic acid and an organophilic macrocycle dissolved in a hydrocarbon solvent for extraction of radium. However, due to the use of expensive chelating agents, this process is expensive and implementation of this process requires extensive pre-treatment to oil field sludges and a substantial length of time for extraction of the radium.
U.S. Pat. No. 5,207,532 teaches a process for chemically treating, physically shearing and separating NORM from deposits by slurrying the NORM-containing material and treating the resulting slurry with an oxidizing agent, in particular chlorine dioxide, chlorine, hydrogen peroxide, sodium hypochlorite, sodium chlorite, and sodium perporate. In accordance with one embodiment, the slurry of deposits is treated to render the large non-radioactive particles therein free flowing with respect to the smaller radioactive particles, which large non-radioactive particles are removed therefrom, for example, by screening, thereby leaving behind a reduced mass of NORM for disposal.
U.S. Pat. No. 4,146,568 teaches a process for reducing the radioactive contamination in waste product gypsum in which the gypsum is reacted with a dilute sulfuric acid containing barium sulfate to form an acid slurry at an elevated temperature. The slurry is cooled and the acid component is separated from the solid. The resulting solid is separated into a fine and a coarse fraction, the fine fragment being predominately barium sulfate and radioactive contamination. In accordance with the teachings of this patent, the barium sulfate is employed as a radium sorbent. Similarly, U.S. Pat. No. 3,896,045 teaches a process for extracting radium from liquids using a barium sulfate/barium salt sorbent. In particular, the liquid is contacted with sorbent in a sulfate-containing medium of a barium salt or a barium salt mixed with the metal ferrocyanide to which sulfuric acid is added to promote sorption of the radioactive ions.
U.S. Pat. No. 4,328,193 teaches a process for separating radium from monocalcium phosphate solutions by centrifuging the solutions to separate a portion of radium-containing contaminants from the solution and treating the remaining solution with sulfuric acid to produce a phosphoric acid solution and calcium sulfate product containing radium.
U.S. Pat. No. 3,949,047 teaches separation of radium from phosphate ores by reaction of a monocalcium phosphate-containing solution with at least one soluble barium compound in the presence of sulfate ions, resulting in co-precipitation of contaminant radium ions which would otherwise be precipitated with the calcium sulfate.
Finally, U.S. Pat. No. 4,423,007 teaches a process for removal of radium from a radium-containing aqueous solution which contains dissolved magnesium by adding soluble barium salt to precipitate radium sulfate. An insoluble magnesium compound is then precipitated which collects the sulfate. Thereafter, the precipitates are separated from the solution.
Of the aforementioned prior art, only the teachings of U.S. Pat. No. 4,973,201 and U.S. Pat. No. 5,207,532 are applicable to insoluble barite scales found in oil field sludges and soils. However, each of these patents teach a process which is less efficient, and in one case more expensive, than the process of this invention as described hereinbelow.